Eccentric drum mount for revolvertype firearms



w. E. BACKER 2,982,184 ECCENTRIC DRUM MOUNT FOR REVOLVER-TYPE FIREARMS May z, 1961? Filed Sept. 25, 1959 INVENTOR.

@025x www United States Patent Oce t 2,982,184 Patented May 2,1961

ECCENTRIC DRUM MOUNT FOR REVOLVER- TYPE FIREARMS William E. Backer, Fulton, Mo., assigner `to the United States Of America as represented by the Secretary of the Army Filed Sept. 23, 1959, Ser. No. 841,911

2 Claims. (Cl. 89-155) This invention relates to revolver-type machine guns and cannons, such as the U.S. Automatic Revolver Firearm, M39, and more particularly to means for mounting the revolving drum so as to compensate for the misalignment of the chambers therein with the axis of the barrel bore during operation of the gun.

Considerable trouble has been experienced with highpowered and rapid-firing revolver-type firearms, such as the M39, because of the transient misalignment of the drum chambers with the barrel during firing operation. This misalignment is serious because it causes the projectiles from the discharged cartridges in the drum to enter the barrel bore angularly relative to the axis thereof and thereby cause balloting which shortens considerably the life of the barrel. Also, the projectiles are damaged by the nonuniform contact thereof with the `barrel bore when propelled into the barrel to cause erratic ight therefrom.

Moreover, this misalignment causes the front faces of the obturating seals slidingly carried by the chambers to incompletely contact the breech face of the barrel, permitting leakage of the discharge gases between the seals and barrel to cause serious erosion thereto.

It has been discovered that, through this transient misalignment, the axis of the drum chamber in the ring station drops approximately .D-.015 of an inch below the axis of the barrel when the gun is tiring and this misalignment is attributed in large part to a transient deformation of the drum supporting cradle through eccentric stresses set up therein by the recoil forces transferred thereto from the drum and to nonuniform thermal expansion of the cradle.

It is, therefore, an object of this invention to provide means for mounting the drum to the cradle for a predetermined misalignment of the ring station chamber with the barrel bore, when the gun is not being fired, so that during gun operation such chamber will become correctly aligned with the barrel.

It is another object of this invention to provide a bushing mountable in the front support of the cradle in which bushing the bore for receiving the drum shaft is disposed eccentric to the outside periphery of the bushing for displacing the front end of the drum from axial alignment with the barrel bore a distance equal to the predetermined drop of the front end of the drum during gun operation to compensate for such drop.

The specific nature of the invention as Well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a top view of the U.S. Automatic Revolver Firearm, M39;

Fig. 2 is an enlarged view taken along line 2-2 of Fig. 1;

Fig. 3 is a view taken along line 3-3 of Fig. 2; and

Fig. 4 is a perspective view of the bushing.

Shown in the figures is the U.S. Automatic Revolver Firearm, M39, having a longitudinal channeled receiver 12 in which there is mounted a drum cradle 14. Drum cradle 14 includes a longitudinally `disposed base portion 18 and a front support 20 and a rear support 22 which extend integrally upward therefrom. Slidingly supported by the front end of receiver 12 is a `barrel 24 having a bore 26 the longitudinal axis of which is denoted by center line A--A in Fig. 2. The rear end of barrel 24 is received by a mating opening 28 in :front support 20 and is releasably secured thereto by conventional lug means (not shown).

A shaft 30 is journaled in front support 20 and rear support 22 so as to be disposed parallel to the axis of barrel 24. Mounted on such shaft is a drum 32 which is connected at the rear end to the shaft by spline means 34 so that the shaft and drum rotate together and so that the rear end of he drum is Coaxially supported by the shaft.

The front end of drum 32 is rotatingly supported by a bushing 36 which is rotatingly received by a counterbore portion 38 extending axially into the drum from the front end thereof. Bushing 36 includes an aperture 40 having the same diameter as the section of shaft 30 which is adjacent the front end of drum 32 so that the shaft may extend through the bushing for support thereof. Provided around the outside of bushing 36 is a cylindrical bearing surface 42 having the same diameter as counterbore 38 sothat the bushing is receivable therein to provide bearing support for drum 32. An integral plate 44 at the front end of bushing 36 is joined by T-slot means to front support 20 to prevent rotation and axial displacement of the bushing.

Drum 32 `is provided with live chambers 46 each being adapted'tocarry a cartridge 48 into registry with bore 26 when the drum is rotated and each having an axis as noted by center line B-B in Fig. 2. Drum 32 is rotated to successively position the chambers 46 in registry with bore 26 through the cooperation of five rotary followers 50 disposed around the Outside of the drum with a cam path 52 formed in a slide 54 mounted in receiver 12. Slide 54 is disposed for reciprocation responsive to the forces produced by the discharge of cartridge 48 in the barrel aligned chamber 46.

Coaxially mounted in each of the chambers 46 is` an obturating sleeve S6 having a front face 58 which is disposed for full contact with the breech face of barrel 24 when the supporting chamber.` 46 and the barrel are aligned. The one of the sleeves 56 in the barrel aligned chamber 46 is slidingly extendable from drum 32 for contact with the breech face of barrel 24 responsive to the pressure of the discharge gases against the rear face of the sleeve. Whereby, the space between the barrel aligned chamber 46 and the breech face of barrel 24 is bridged to prevent leakage of the gases produced by the discharge of cartridge 48 in such chamber when the front face of the sleeve in such chamber is in full Contact with the breech face of the barrel.

When the gun is tired, the eccentric stresses produced in drum cradle 14 cause the front end thereof to drop between .010 and .015 of an inch. Therefore, in order to have axis B-B of the one of the chambers 46` in registry with bore 26 align with axis A-A thereof during operation of the gun, cylindrical bearing surface 42 is formed eccentric to aperture 40 the predetermined distance which the front end of drum 32 is dynamically displaced during 3 42. Thus, the axes B-B of the chambers 46 in registryr with barrel 24 are aligned with the axis A--A of bore 26 during operation of the gun. The eccentric relationship between aperture 40 and bearingsurface 42 may be adequately determined by averaging the displacements of the chambers 46 in several guns of the same model. However, if precision is desired, aperture 40 should be eccentrically disposed according to the operating characteristics of the individual gun in which bushing 36 is to be installed.

Alignment of axis B-B with axis A-A is determinable by a study of the bore markings on the recovered projectiles. When the engravings on the projectiles are uniform, the axes A-A and B-B are in proper alignment.

From the foregoing it is clearly apparent that there is provided herein a simple and effective means of overcoming a very serious problem inherent in revolver-type automatic firearms which means include a bushing with a predetermined eccentricity to initially misalign the drum respective to the barrel axis so as to compensate for the expected displacement of the drum chambers during operation of the firearm. Thus, the projectiles of the cartridges discharged in the drum enter the barrel bore along the axis thereof to eliminate balloting therein and the front faces of the obturating seals fully contact the breech face of the barrel to prevent gas leakage and consequential erosion.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

I claim:

1. In an automatic firearm, a receiver, a cradle mounted on said receiver, a barrel replaceably mounted on said cradle, a drum mounted on said cradle for rotation adjacent the breech end of said barrel and provided with chamber means for successively carrying cartridges into registry with said barrel for discharge thereinto, said cradle being subjectable to the forces produced by the discharge of the cartridges to deflect said drum a predetermined distance relative to the axis of said barrel during operation of the firearm, and means for misaligning said drum relative to said barrel when the firearm is inoperative to compensate for the predetermined distance which said drum is deflected when the firearm is operated and thereby axially align the chamber means with said barrel when rotated thereto during operation of the firearm.

2. In an automatic revolver firearm, a receiver, a cradle mounted on said receiver, said cradle including a front support and a rear support, a barrel replaceably mounted on said front support, a shaft rotatingly mounted between said front and rear supports, a drum mounted on said shaft for rotation adjacent the breech end of said barrel, a plurality of chambers disposed in said drum for successively carrying cartridges into registry with said barrel for discharge thereinto, said cradle being subjectable to forces produced by the discharges of the cartridges to deliect the front end of said drum a predeterminable distance and thereby misalign said chambers from said barrel when rotated into registry therewith, and a bushing mounted in said front support and provided with an aperture for rotatingly supporting the front end of said shaft, said aperture being eccentrically disposed in said bushing relative to the outside periphery thereof a distance equal to the predeterminable distance which the front end of said drum is defiected by the discharge forces to compensate for such deflection and thereby axially align said chambers with said barrel when rotated thereto during operation of the firearm.

No references cited. 

